Demodulating means



April 1l, 1939. l H, cHlRElx 2,153,512

DEMODULATING MEANS originalFiled Feb. 12, 1955 2 sheets-sheet 1 0in-'cran 1 /0 ATTORN EY April 11, 1939. H. @HIREIX DEMODULATING MEANS Original Filed F'ebl l2, 1935 2 SheetS-Shee'tI 2 INVENTOR HENRZH/RE/X w@ f ATTORNEY Patented `pr. lll, 19x39 PATENT OFFICE 2,153,612 v DEMoDULA'rrNG MEANS y,

Henri Chireix, Paris, France, assigner to oxnpagnie Generale De Telegraphie Sans Fil, a

` corporation oi' France Original application February 12, 1935, Serial No.

Divided and this application June 18,

1937, Serial No. 148,834. In France February z (ci. 11a-ss).

The presentA applicationwhich is a division of my United States application #6,137, iiled February` 12, .1935, now Patent #2,135,171, dated November 1, 1938, concerns novel devices adapted to 5' be used in signal reception which in addition are suited to insure a system of secret transmission useful for communications over telephone wires or cables, telegraphy through ground, and telegraphy by Hertzian waves. y

Independently of the usual means consisting in the use` of a code, secrecy is assured according to the present invention by the particular method oi transmission and reception.

It is known that one of the most widely used signalling methods consists in the transmission of musical or tonal, audio frequency currents, these currents being interrupted or chopped by a key in accordance with a certain code, say, the Morse code.

It is also known that it is possible to key by causing a current known as the working current to flow on a certain frequency,-and another current known as the rest or spacing Vcurrent to flow on another frequency.

It is also known that it is possible to combine in one and the same frequency the working and thespacing transmissions by causing by the key certain variations of phase in the modulator current.

The invention is concerned with this latter mode of signalling, and it discloses new means of receiving signals transmitted in this way.

As a matter of fact, according to the prior art it has been necessary to provide at the receiving station a current absolutely in synchronism with the outgoing current so as to bring out and make noticeable the variations in phase. Indeed, the maintenance of synchronism necessitated the transmission ofy synchronizing signals, and this is liable to involve serious inconvenience from the f viewpoint of synchronism andof insuring secrecy of the methodjthat is employed. Now, thev present invention dispenses with the s necessity of strict synchronism and `therefore oi the sending of synchronizing signals orthecon- `tinuation of `tra'nsrn'ission outside the actual oper- .ating` periods. It`disclosesmor'e particularlytwo practicalem- 'bodimen'ts these two 'embodiments being predicated `upon thause oi one and the samebasic invention which is as follmis:`

' The, tranSniSSi 1.1 0f @Urrent lb'ns:iriSfiilVt-d by means 'of a' icurrent generated' by `they of a 'l (tuning fork, for instance, 'jandjsuitably' amplied,

JV y this current, 'at the receivingendQis caused 'to beat with poly-phase currents produced, for instance, by anotherwtuning fork and, according to wellknown methods of heterodyne reception,- the said receiving tuning fork vibrates with very close approximation at the same frequency (say, within 5 one-thousandth) What results beyond the detectors is a polyphase current having the ,very low frequency of the beat. With poly-phase cur rent there is produced a rotatingK field byways and means generally known in the art.

This eld will turn in either sense according to the vsense of the asynchronism, or else will not rotate at all during the intervals of time where iscchronism is attained.

Keying `is eiiected by means of variations of phase, that is to say, by advancing an angle 0 to characterize a working transmission and retarding it a similar angle for spacing..

The rotating eld just referred to 'will be shifted forward or caused to lag the same angle no matter what the position of its axes at the instant in question. For a working" transmission or signailing it may turn, for instance, in the sense of the clock, while for spacing it will turn anticlockwise.

These rotations are used for decoding the transmitted text by means of one from among t'wo arrangements hereinafter described by way of example. In describing these arrangements reference will be made to the'drawings in which Fig- 30 ures 1 and 2 are circuit diagrams including the essential elements of my phase rotation analyzing circuits, while Figures 3, 4, 5, and 6 show details of recordingI or indicating devices which may be used to record or indicate the output of Figure 2.

I and 2 represent in Figure 1 the tubes of a twin symmetric or push-pull system. Each system 'may comprise two triodes or tubes of a more improved type comprising, for instance, tubes havingn two control grids; For the sake of simplicity there is yshown for each system one tube equivalent to two separate triodes;V The `four gridsare biased at the initiation of the plate current by the source 3 and `excited in parallel by the modulation to be received by' means of transvformer l. n

They are .moreover excited by pairs in Opposition'by the twophases of atwo-pliase alternator 5 whose frequency isvery closelylthe same'as the frequency of the currents tobereceived. There is thus vinsured detection b y virtue or the lower knee in the plate characteristic.

Thecircuits ofthe plates are constituted by the resistances 6 being preferablyequal and shunted 'bycondensersi and inserted betweeiitheanodes and the high voltage source connected at 8. The plates are moreover connected with the four deiiector plates 8 of a cathode-ray tube. The part and purpose of the condensers 'I being to shortcircuit the alternating current components of high frequencies of the. plate current, there is obtained between Athe two deflecting plates of a system of plates an electrostatic alternating iield of very low frequency due to the beats between the modulation to be received and the local generator. The cathode pencil subjected to two alternating fields of this kind will thus turn very slowly, and the spot upon the uorescent screen will describe, for instance, very slowly a circle if the amplitudes are alike. Indeed, if isonchronism is present or attained during a more or less long period the spot will be reduced to a fixed point 'upon this circle, and the spot will be shifted in one sense or the other as soon as isonchronism ceases. If the currents received by the transformer 4 are modulated in phace as has been stated, the modulation being translated in a4 phase displacement of 20, then the spot will shift very rapidly, 4for instance, the clockwise sense at thel instant a signal is4 sent and will return in the opposite sense at the instant spacing begins. Owing to the visual persistence of the retina, keying will -be seen in the form of lines of like, lengths, but succeeding one another at unequal intervals according to whether short dots or long dashes are involved.

It will be noted that if the transmitter Ais stopped the spot naturally will comeY to be located in the center of the screen. From the linstant of start, with the key in the beginning being blocked vfor spacing, the spot will appear at any point at all of the circle and at the first signal it will describe in a. predetermined sense a rotation 20.

Hence, there exists no ambiguity, and the reading of the message may begin at once.

The second embodiment here disclosed involves a receiver apparatus which is more practical in actual use and allows of actuating a relay so as to be able to record the transmitted text in the usual Way. 'I'here is employed a special relay conceived in a way as indicated in Figure 3 and fed Afrom an electromagnetic rotating eld as soon as a state of asynchronism is established.

This rotating field could'be produced in accordance with the scheme shown in Figure 2 where 5 represents a-local two-phase generator comprising phases a and b, III detectors of the copper l oxide type, for instance; II resistances, Ila and Mb windings wound V-IashiOn, for instance, corresponding to the phases a and b resulting in the rotary field, I5 capacitiesfshunting these windings, and finally, the source of modulated waves connected with the input terminals. It will beV seen that a detector element such as I is subject` to the potential 'resulting from a phase oi the local generator and the reception. One of the windings, for instance Ila, will thus be traversed by a maximum current of definite direction when `the incoming energy has the phase of a while the current will be of zero value when the phases are in. quadrature since the potentials are vthen gemetrically equal at the terminals of the two detectors in the phase. The current in Ila will then again be of maximum value, but will be opposite in direction compared with the preceding one, when there is phase opposition between the incoming energy and phase a.

Hence, the current in Ila varies in accordance with a sine law, according to the phase of the incoming energy compared with the phase a. The same situation holds true regarding the current in 'Mb except that the current will be of zero value in IIb when it is at its crest value in Ila because of the' fact that the law of variation is here of sinuous form shifted an angle of 90 degrees because the incoming energy is combined here with the phase b being in quadrature with the phase a. The currents in Ila and IIb are therefore endowed with all of the qualities required to feed a rotating field system such as 4rotating field system, Figure 2. These windings are accommodated in the slots of a rotor I2, the current being fed by way oi rings I3. Each of the systems, there being two, of Figures 3 to 6 contains four loops located in pairs of parallel vertical planes; the horizontal sides of one pair of loops are one-half as long as 'the horizontal sides of the other pair of loops. The system comprises two identical but perpendicular groups of windings of this type. 'I'he Vertical sides of the adjacent loops comprising the diilerent windings pass through. common slots, there being eight slots per rotor. N

The rotor turns in the interior of a stator constituted by two sets of curved magnets I6 having polarities of the same nature N and S placed opposite each other, and pole pieces such ,as indicated at I1 forming between themselves an air-gap.

In the air-gap of these pole-pieces is disposed a magnetized needle I8 presenting poles such as n and s. 'I'his needle is pivoted directly at I9 on the peak of the rotor I2, it constitutes the keeper of a polarized relay; its stroke is limited either Way by stops on contacts such as indicated at 20.

'2| denotes nally regulating springs of the l coincidence between the line of the poles of the rotor and the line of the poles of the magnets I6. When the position of equilibrium has been reached, the needle I8 is positioned. on a line of symmetry of the flux. As long as the state of isochronism is maintained the rotor will not move; but as soon as the saidstate ceases to existthe rotor will turn slowly in either sense. If keying then takes place by virtue of the variation of the phase by an amount i0 compared with the mean phase the rotor will not be driven because of its high (relative) inertia, but the far lighter needle will respond to the keying.

From the instantaneous viewpoint, as a matter of fact, the rotor ileld will be phase-displaced by i@ degrees. Under these conditions the flux of the rotor will be closed by the magnets II by traversing the air-gaps formed between the polepieces I1 and the needle I8 will be shifted under the action of this flux. I

It could also be said that the instantaneous displacement of the field creates in the opposite pole-pieces I'I supplementary poles n and s, or s and n which destroy the symmetry of the lines of force. It is evident that if the keying is ir- I aiaoia regular the line of the poles n. and s will not be positioned exactly in the center of the arc amounting to 20; but this is immaterial, in fact, one could even stay on a continuous dash or a space provided that the' angle 0 is not chosen too large (0 90 degrees). If, for instance, there is chosen 20:90 degrees and staying on space, the instantaneous torque will be of maximum value at the instant work is started, because the polar line will then be caused to turn suddenly an angle of degrees, and since the. entire flux of the -lrotor will become closed in the air-gaps of the pole pieces I1. If one keys thereafter in a regular manner', the rotor will be displaced 45 degrees approximately and present a position as indicated in Figure 4. If the state of isochronisrn is not exact, the rotor will be shifted more according to the ship frequency which, however, is always very small. It will be understood that it is desirable to make the rotor relatively heavy in order that it may not be driven along. The springs 2|, 2I moreover should be so regulated in order that in the absence of transmission the needle may be in equilibrium (unstableY in the air-gaps of the pole-pieces Il.

It will evidently be 'possible to have recourse to the contacts of the relays to operate a recorder with tape or simply for closing the circuit of a telephone fed from the local oscillator. In this latter instance there is thus preserved the advantage of reception by ear.

It will be noticed that the circuit arrangements hereinbefore disclosed are directly useful with high frequency and may be employed under particularly favorable conditions in telegraphic communication on long waves. It is very likely, indeed, that by the aid of tuning forks frequencies that are stable to within Momma may be obtained, f

in other words, that on waves greater than 3000 meters it is possible to insure an asynchronism whose frequency will not be over two beats each second. By using circuit arrangements as hereinbefore-disclosed together with apparatus of a kind as described, it will be feasible to handle trailic under conditions far better than under present day conditions. As a matter of fact, it is well known that. from thevlew point of disturbances, atmospherics and jamming, keying and signalling predicated upon phase shifting insures a maximum degree of immunity,

l Although in the exemplified embodiments h'ereinbefore illustrated recourse is had to two-phase fields, it is evident that the invention is equally applicable to any other multi-phase elds.

It will be evident, on the other hand, that other dispositions predicated upon the same basic idea rotor, said permanent magnet comprising a plucould be considered. More particularly speaking, in the second solution it could be conceived that the light needle designed to respond to and follow the keying is subjected to a turning field inde- -pendent of the former, though connected with it IY l mechanically. ,i

For instance, the rotor could be made heavier and the stator could be divided into two parts, one constituted by magnets such as I6 whose purpose, as above pointed out, is to orientate -the rotor flux, and another consisting of non-magnetized magnetic pieces supporting the poles I l and designed to collect the ux of the rotor when the lines of the poles are displaced under the action of keying. This arrangement has the advantage over the preceding one of shifting the mobile needle IBin an air-gap not permanently magnetized. This modification is illustrated in Figure 6. .The 4rotor I2A of the relay comprises slots or grooves in which are placed windings I4 of the rotary-field system. the current being fed by way of the rings I3.

Upon the casing 22 of the stator are mounted,

non the one hand, the magnetic pieces I1, and

these are of the same form as the pieces IG--II in Figures 3 to 5. They enclose between themselves an interferric space in which is mounted a needle or pointer I8 pivotal on the end I9 of the rotor. The latter is suiliciently heavy so that its ilux will embrace the pieces I6 and I1. The mechanism of the contacts between which the needle moves is the same as inFig-ures 3 to 5.

I claim:

l. A device for producing indications of the rotation of an electrical eld produced by phase modulations on a carrier wave comprising. `a support member, a slotted rotor mounted for rotation in said support. iield producing windings in the slots of said rotor,-a permanent magnet enclosing an additional magnet mounted for rotation between said pole pieces.

2. In a device for producing indications of the rotation of an electrical eld produced by phase modulations on a carrier wave, a support member, a rotor mounted for rotation in said support member, field producing windings supported by said rotor, a permanent magnet adjacent said rality of adjacent pole pieces of like polarity. an indicating magnet mounted for movement between said pole pieces, and resilient means tending to hold said additional magnet in a predetermined position. .n 5I 

